This is the 149th most frequent Russian word.
александр
"Alexander" - a male given name.
Here, 'Александр' is a proper noun used as the subject of the sentence, referring to a person's name.
Александр любит ходить в парк.
Alexander likes to go to the park.
In this sentence, 'Александр' is in the accusative case, 'Александра', indicating whom the action is directed towards.
Мы позвали Александра на праздник.
We invited Alexander to the celebration.
Here, 'Александра' refers to a proper noun, and the sentence explains a possible nickname derived from this formal name.